searching an array of classes

If you're using .NET 2.0 or greater, you can do it after a fashion with code like this:

using System;

class Test
{
    static string matchUserName;

    static void Main()
    {
       MyClass[] myArray = new MyClass[3];
       myArray[0] = new MyClass("Fred Bloggs", 12);
       myArray[1] = new MyClass("Bob Smith", 25);
       myArray[2] = new MyClass("Jack Jones", 42);
       matchUserName = "Bob Smith";
       MyClass mc = Array.Find(myArray, MatchesUserName);
       if (mc != null)
       {           
          Console.WriteLine("The UserId for {0} is {1}", matchUserName, mc.UserId);
       }
       else
       {
          Console.WriteLine("{0} is not in the array", matchUserName);
       }
       Console.ReadKey();
    }

    private static bool MatchesUserName(MyClass mc)
    {
        if (mc.UserName == matchUserName)
        {
            return true;
        }
        return false;
    }

}

class MyClass
{
   private string userName;
   private int userId;

   public string UserName
   {
      get {return userName;}
   }
 
   public int UserId
   {
      get {return userId;}
   }

   public MyClass (string userName, int userId)
   {
      this.userName = userName;
      this.userId = userId;
   }
}